connectd: rescue constant message size feature by exploiting OPT_ONION_MESSAGES (LND)

rustyrussell · sangbida · commit 52b70043ab26 · 2026-04-10T14:53:11.000+10:00
I 🧡 Laolu!

Signed-off-by: Rusty Russell &lt;rusty@rustcorp.com.au&gt;
diff --git a/connectd/multiplex.c b/connectd/multiplex.c
@@ -481,9 +481,13 @@ static bool have_empty_encrypted_queue(const struct peer *peer)
 	return membuf_num_elems(&peer->encrypted_peer_out) == 0;
 }
 
+/* Funny story: we discovered an LND bug, where they hung up if we sent
+ * "no reply" ping messages.  This was fixed in (the upcoming) v21, which
+ * Laolu pointed out also supports onion messages.  Hence we use that
+ * to detect if we should pad packets. */
 static bool use_uniform_writes(const struct peer *peer)
 {
-	return peer->daemon->dev_uniform_padding;
+	return feature_offered(peer->their_features, OPT_ONION_MESSAGES);
 }
 
 /* (Continue) writing the encrypted_peer_out array */

Original file line number	Diff line number	Diff line change
`@@ -481,9 +481,13 @@ static bool have_empty_encrypted_queue(const struct peer *peer)`
`481`	`481`	`return membuf_num_elems(&peer->encrypted_peer_out) == 0;`
`482`	`482`	`}`
`483`	`483`
	`484`	`+/* Funny story: we discovered an LND bug, where they hung up if we sent`
	`485`	`+ * "no reply" ping messages. This was fixed in (the upcoming) v21, which`
	`486`	`+ * Laolu pointed out also supports onion messages. Hence we use that`
	`487`	`+ * to detect if we should pad packets. */`
`484`	`488`	`static bool use_uniform_writes(const struct peer *peer)`
`485`	`489`	`{`
`486`		`- return peer->daemon->dev_uniform_padding;`
	`490`	`+ return feature_offered(peer->their_features, OPT_ONION_MESSAGES);`
`487`	`491`	`}`
`488`	`492`
`489`	`493`	`/* (Continue) writing the encrypted_peer_out array */`